1. Field of the Invention
The invention relates to an image forming apparatus such as printer, facsimile, copying apparatus, or the like or an image forming apparatus such as an MFP (Multi Function Printer) or the like having at least two or more functions of those apparatuses or the like.
2. Description of the Related Art
Among image forming apparatuses represented by a printer, there is an apparatus having a recording head in which recording devices such as exothermic resistor elements, light emitting devices, or the like are arranged in a line or a plurality of lines. In such an image forming apparatus, an image is formed by selectively supplying a current to those recording devices. In the recording head which is used in the image forming apparatus, it is important that characteristics of the arranged recording devices are identical. This is because, for example, in an image forming apparatus using LEDs (light emitting diodes) as light emitting devices which are used in a printer of an electrophotographic system or the like, if light emitting energies of the LEDs to which the same current has been supplied are equal, a uniform image without a deviation which depends on layout positions of the LEDs is obtained. However, it is generally difficult to manufacture the recording devices whose characteristics coincide accurately. Therefore, a characteristics variation of the recording devices is corrected, for example, in the case of the light emitting devices, the energy for recording is corrected by changing a light emitting time or a drive current value (for example, refer to JP-A-1996(Heisei-8)-142406).
A problem to be solved is as follows. In the above energy correction, it is difficult to continuously and smoothly change energy distribution in the scanning direction, and discontinuous points of the energy distribution are liable to occur between the adjacent recording devices. Such discontinuous points are accumulated in dependence on human visual characteristics and appears as a stripe-shaped concentration variation which continues in the sub-scanning direction on an output image.